You could have said the same thing for Arredondo last year (8.15 K/9, 5.26 BB/9) when he put up a 3.26 ERA. Yet his ERA improved this year.
You could have said the same thing for Ondrusek each of the past two seasons, yet his ERA has gone from 3.68 to 3.23 to 3.46. All three seasons Ondrusek has out-performed his ERA estimators. One has to wonder if there's a possibility there are reasons for that.
I don't know what to expect out of Simon, but while his HR/FB ratio is part of the reason for the success, he added almost a full strikeout per inning this year and nearly doubled his GB/FB ratio. While I don't expect a complete repeat of this year's success, if he continues those rates, he'll have another very good year. Any reliever with a 7.5 K/9 and over 2-1 GB/FB rate is going to be pretty successful, typically.